How Does a Dimmer Switch WorkOnce a novelty, dimmer switches have become a common feature in many homes ‒ a simple device that lets you control the brightness of any room. Dimmers let you select the light level best suited to your activity. You can turn them down when watching a movie, then up again while reading a book. They can even help you reduce your energy consumption. There is no room in your house that can’t benefit from one, but how does a dimmer switch work?

Early Dimmer Switches

The first dimmer switch was invented by Joel Spira in 1959. He realized that by lowering a variable resistor over the circuit, he could reduce the flow of power into the light bulb, dimming its brightness. Resistors are materials that don’t conduct electricity. Installing a variable resistor let Spira adjust the circuit’s conductivity. As resistance increased, a large portion of the electricity moving through the circuit was absorbed and converted into heat, which lowered the amount of energy available to the light bulb and decreased its output.

Originally marketed as a romantic appliance, which allowed parents to turn down the lights after the kids went to bed, Spira’s design had a few notable shortcomings. First, it didn’t reduce energy consumption. The switch used the same amount of electricity no matter what level it was set to. Some of it was simply prevented from getting through. Second, the heat it generated wore down the circuit and created a potential fire hazard.

Modern Dimmer Switches

Modern dimmer switches are fitted with a triac power control device, which turns the circuit on and off in quick succession. Household electricity runs on alternating current, whose polarity fluctuates rapidly as it flows through your home. The electrons switch from a positive to a negative charge and back again, reversing direction around sixty times a second.

Every time the switch happens, the triac device momentarily shuts off the circuit. By cutting power at the exact moment the electrons change direction, modern dimmer switches can reduce the amount of energy going into the bulb without causing the lights to flicker. Turning the dimmer up or down determines how long the circuit’s off, which determines how bright your lights are. This prevents heat from building up in the switch while lowering your energy bills at the same time.

Types of Dimmer Switches

Dimmer switches come in several varieties, depending on the design of your home electrical system and the type of light bulbs the switch controls. The three basic set-ups are:

  1. Single Pole. The light is controlled by one dimmer switch.
  2. Three-Way Dimmers. The light is controlled by a dimmer switch, and at least one other switch somewhere else in the room.
  3. Multi-Location Dimmers. The light is controlled by multiple dimmers located in different parts of the house.
  4. Plug-In Dimmers. Used to control table and floor lamps. One end connects to the lamp and the other to the wall socket.

Dimmers are also categorized by which part of the current cycle they cut off. Forward-phase dimmers shut down the circuit in the middle of the cycle, as the electron is losing its charge. Reverse-phase dimmers do the opposite. They shut down the circuit at the beginning of the cycle, as the electron is becoming more charged. Put another way, forward-phase dimmers shut off as the electron is approaching zero while reverse-phase dimmers shut off as the electron is fully charged.

Incandescent and LED bulbs can be controlled by forward-phase and reverse-phase dimmers. However, an MLV (Magnetic Low Voltage) bulb is only compatible with forward-phase dimmers, while ELV (Electric Low Voltage) bulbs are only compatible with reverse-phase units. MLV bulbs are typically used in recessed lighting. ELV bulbs, on the other hand, are normally used in work lights or under-cabinet lighting.

If you don’t know what type of lights you have in your home, you can always install a universal dimmer, which works with all types of lighting. Along with a triac, they also contain microcontrollers. Once you set the selector switch, the dimmer detects which type of bulb they’re connected to and adjusts their operation accordingly.

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